1. Field of the Invention
The present invention relates to a method for detecting a motion signal of a video signal which searches motion information in the video signal, and also to a video signal processing apparatus using the same method.
2. Description of the Related Art
Heretofore, in a television receiving set or image special effect equipment for generating special effect images by changing the images by performing enlargement, contraction, rotation, or the like on video data, processing intended to improve the picture quality is carried out by converting an interlaced scanning video signal into a non-interlaced scanning video signal. More specifically, an interpolation scanning line is provided between the scanning lines of the non-interlaced scanning video signal to thereby generate the non-interlaced scanning video signal, with the result that the vertical-direction resolution of the video signal is improved and the flicker of the displayed picture is controlled.
In the above method, for the video signal of a still image, an interpolation scanning line is generated by data of the previous field, and for the video signal for a moving image, an interpolation scanning line is generated by data of the current field. In order to convert the interlaced scanning video signal into the non-interlaced scanning video signal, motion information in the video signal must be detected, and according to the result of this detection, the generating method of the interpolation scanning line must be changed.
with regard to the technique for detecting motion information of the interlaced scanning video signal, various methods have been proposed. In most of those methods, motion information is detected in pixel units depending on the magnitude of a difference signal between the input video signal and the video signal delayed by one frame. Such a method for detecting motion information is described at pages 211 to 212 of the prepared papers for the 1989 National Convention of the Institute of Television Engineers of Japan.
FIG. 4 is a block diagram showing an example of a conventional motion signal detection circuit. In FIG. 4, reference numeral 1 denotes a video signal input terminal, 2 a one-frame delay circuit, 3 a subtractor, 4 a low pass filter, 5 an absolute value calculating circuit, 6 a maximum value calculating circuit, 7 a coring control circuit, 8 a low pass filter, 9 a vertical edge detection circuit, 10 a time-space expander circuit, and 11 a motion signal output terminal.
The operation of the above-mentioned prior-art circut will now be described.
In FIG. 4, the video signal input from the video signal input terminal 1 and the video signal delayed by the one-frame delay circuit 2 undergo a subtraction process by the subtractor 3 to obtain an inter-frame difference value. The inter-frame difference value is deprived of noise by the low pass filter, and an absolute value is calculated by the absolute value calculating circuit 5. For the calculated absolute value, a maximum value nearest in terms of time and space is selected by the time-space expander circuit 10 and the maximum value calculating circuit 6. The selected maximum value is subjected to a coring process according to the vertical edge intensity of the input image by the vertical edge detection circuit 9 and the coring control circuit 7. In this prior-art example, the portion with a great vertical edge of the image receives a process similar to the process for a still image. The absolute value after the coring process is further deprived of noise by the low pass filter 8, and is output as motion information to the motion signal output terminal 11.
However, in the motion signal detection circuit, the condition for deciding whether to classify the picture portion as a "motion" or "still" portion is determined by a parameter of the coring control circuit 7 and, therefore, a motion signal having an inter-frame difference signal of the same level as noise cannot be detected.
In order to solve the above problem, a motion detection method using a target pixel for detecting motion information and the pixels in a space surrounding the center target pixel has been proposed. A motion signal detection method such as this is shown in Tanaka et al. "Processing Frame Difference Signals for Detection of Moving Areas", Technical Report of the Institute of Television Engineers of Japan, Vol. 10, No. 12, pages 59-64, for example.
FIG. 5 is a block diagram showing another example of the conventional motion signal detection circuit. In FIG. 5, reference numeral 1 denotes a video signal input terminal, 2 a one-frame delay circuit, 3 a subtractor, 12 a space expander circuit, 13 a plus/minus pixel number calculating circuit, 14 a moving amount calculating circuit, and 15 a motion signal output terminal.
The operation of this other prior art example will now be described.
In FIG. 5, the video signal input from the video signal input terminal 1 and the video signal delayed one frame by the one-frame delay circuit 2 undergo a subtraction process by the subtractor 3 to find an inter-frame difference value. The inter-frame difference value is output by the space expander circuit 12 along with the inter-frame difference signals at the pixels in a space surrounding the center target pixel. In this prior-art example, the inter-frame difference values at 5.times.5 pixels in a space surrounding the center target pixel are calculated. With regard to those inter-frame difference values, the total number of pixels p having positive difference values and the total number of pixels n having negative difference values are calculated. Then, the moving amount calculating circuit 14 calculates a motion evaluation value .alpha. from the numbers p and n mentioned above as shown in the following: EQU when p.ltoreq.n .alpha.=p/n EQU when p&gt;n .alpha.=n/p EQU 0.ltoreq..alpha..ltoreq.1
Accordingly, the moving amount 1-.alpha. is output from the motion signal output terminal 15.
The operation of the moving amount calculating circuit 14 will now be described with reference to FIG. 6. FIG. 6 shows an example of the inter-frame difference signal output by the subtractor 3 of FIG. 5.
In FIG. 6, the dotted line denotes a fundamental inter-frame difference signal when there is no noise, while the solid line denotes an inter-frame difference signal added with noise. When the inter-frame difference signal in FIG. 1 is expanded in space and then the p and n are calculated, the p and n become substantially the same number in the still-image region. Therefore, the motion evaluation value .alpha. comes closer to 1, and a moving amount close to 0 (still) is output. In the moving-image region of FIG. 6, a difference between p and n is large. Accordingly, the motion evaluation value .alpha. approaches 0, so that a moving amount (motion) close to 1 is output.
As has been described, in the above-mentioned one other example of the conventional motion information detection processing method, it is possible to detect a motion signal having the same level of an inter-frame difference signal as is caused by noise.
However, in the above-mentioned motion signal detection method, with regard to the video signal obtained when an object having a fine pattern moves in parallel translation, motion cannot be detected. To be more specific, when the inter-frame difference signal of the video signal such as mentioned above is calculated, like in the still-image region of FIG. 6 showing the other prior-art motion information detection method, the p and n become almost the same number and, therefore, a result of motion information detection indicates a wrong recognition that the image is "still", and a moving amount close to 0 is output.